Members that are subject to repeated stress, such as power transmission components of automobiles (for example, toothed components such as gears or splines used in final gears of transmissions, drive shafts, etc.), are required to have not only excellent power transmission efficiency but also features such as high fatigue strength and low noise. It is therefore regarded as important to improve dimensional accuracy in the part of contact between members.
Members required to have high dimensional accuracy have conventionally been formed by machine cutting, but this has the disadvantage of longer processing time and higher manufacturing cost. Hence, cold forging that achieves excellent dimensional accuracy of the formed product has been increasingly used in recent years. Moreover, a component formed by hot forging and a component formed by cold forging differ in characteristics of the finished component. The cold-forged component, in which fiber flow is formed, tends to have excellent component characteristics.
For example, Patent Literature (PTL) 1 proposes a method for manufacturing a tooth profile component by stretch-forming an initial tooth profile by cold forging and then forming a tooth tip to project from the initial tooth profile by cold forging.
PTL 2 proposes a manufacturing method whereby a material inserted in a die is sandwiched between a punch and a knockout with a predetermined pressing force and, in the sandwiched state, the raw material is formed into a component by applying an axial pressing force that is larger than the sum of a knockout pressing force and a forming pressing force to the punch while rotating the punch, thus enhancing forming accuracy even in the case where the component has a large twist angle.